Hi Justice
My suggestion would be to make the fields and queries varchar and not numeric.
Then try the following query to detect the text in OpeningReading and bring back the text or do the calculation:
SELECT CASE WHEN $[DLN1.U_OpeningReading.0] NOT LIKE '%[A-Z]%' THEN $[DLN1.U_OpeningReading.NUMBER] - $[$38.11.NUMBER] ELSE $[DLN1.U_OpeningReading.0] END
Kind regards
Peter Juby